Presentation on theme: "Transformation of Water (H 2 O) The measure of the average energy of motion of the particles substance TEMPERATURE m.au/schools/cw/au_sch_whal."— Presentation transcript:
Transformation of Water (H 2 O)
The measure of the average energy of motion of the particles substance TEMPERATURE m.au/schools/cw/au_sch_whal ley_sf1_1/int/2_slg.html Animation- particles and movement
The measure of the average energy of motion of the particles in a substance TEMPERATURE Image Source:
States or Phases of Water The Phase or State of matter is a physical characteristic. describes a PHYSICAL state of matter. As matter changes from one state or phase of matter to another, a physical change occurs. If energy is added (like increasing the temperature or increasing pressure) or if energy is taken away (like freezing something or decreasing pressure) those are physical changes.
w/au_sch_whalley_sf1_1/int/2_slg.html Animation- particles and sublimation
Changes in state are physical changes Image source: Every substance contains energy from the movement of its particles, called thermal energy. The higher the temperature of a substance, the greater its thermal energy.
Requires energy from environment Releases energy to environment
Temperature (degrees Celsius) Time (minutes) Time- Temperature Graph for Water As the temp approaches melting point temperature, the KE of the water molecules increases loosening the bonds between water molecules. As the ice begins to melt, additional heat energy does not raise the temperature of the water, but loosens the bonds changing ice to water. i.e. phase change – melting. Once the water is in a liquid phase, increasing the amount of heat input raises the temp of the liquid water. As the temp approaches boiling point, the KE of the molecules is sufficient to allow the separation of molecules into the gas phase. As the liquid begins to boil. Additional input of heat energy does not raise the temperature of the water, rather it is used to break water bonds. i.e. phase change. Once the water is in the gas phase, additional heat input raises the temperature of the water vapor Note: greater energy is needed to vaporize water than to melt it. WHY?
Phase Change- Melting energy from stove = energy required for phase change NO temperature change Phase Change- Vaporization Energy from hot plate causes increased KE and increased Temperature Energy from hot plate causes increased KE and increased Temperature Two states of Matter One state of Matter Energy from hot plate = energy required for phase change No temperature change
Phase Diagram of Water Energy used to loosen bonds; No change in temp. Energy used to break the bonds; No change in temp. Energy causes particles to vibrate
Lab Demo. A Soluble Problem Summary: Define the terms soluble and insoluble. Soluble Insoluble DISSOLVED
Lab 1: SOLUBILITY What are solutes, a solvents and a solutions? Does stirring help solutes to dissolve? METHOD 1. Place one of the candy pieces in your mouth without chewing or moving your tongue around. 2. Record the time that it takes for this candy piece to dissolve. 3. Place a second candy piece in your mouth, this time moving your tongue, but not chewing. 4. Record the time it takes to dissolve this candy piece. 5. Place the third piece of candy in your mouth and chew it. 6. Record the time to dissolve this third piece of candy. Time (sec) Dissolving Mixing Chewing
2. Copy and complete the following sentences using the words below: Solutionsolventsolutesaliva dissolvesexposedsaliva The candy dissolves in the ……………………..in your mouth to form a liquid ………………………….. Solutions contain two parts, a ………………….. and a ………………………………. The solvent is …………………….. and the solute is the candy. The solute……………………….. by spreading out evenly throughout the solvent. The candy can quickly dissolve when it is ……………… to chewing and stirred by moving it around with the tongue.
Lab 2: ANOTHER STIRRING PROBLEM How does stirring help solutes to dissolve? METHOD 1. Measure 100mL water and place this in a beaker. Prepare two (2) setups. 2. In one beaker, add 1 spoonful of sugar. 3. Record the time it takes to dissolve the sugar. 4. In the other beaker, add 1 spoonful of sugar. 5. Stir until the sugar dissolves. 6. Record the time it takes to dissolve the sugar. Time (sec) No Stirring Stirring Explain your results: Answer the aim.
It All Depends on the Temperature Aim: Why do many substances form solutions more easily in hot water than cold water? Materials: 2 small beakers hot water food coloring METHOD 1.Fill one beaker with cold water. 2. Fill the other beakers with hot water. 3.Wait one minute for the water to calm. 4.Add one drop of food coloring to each. 5.Record your observations over the next 5 minutes. Note: DO NOT MOVE THE BEAKERS GUIDE QUESTIONS: 1.How does the temperature seem to affect the rate of mixing? 2.How is the warm solution different from the cold one? 3.Describe what is happening in terms of particle movement. 4.Draw a dot sketch of each solution. Use more dots to show areas where there is a high concentration of food coloring and fewer dots for low concentration.
Mixtures and Solutions
Molecules are small groups (2 or more atoms) of atoms.
Compounds are pure substances made of 2 or more elements chemically joined together (bonds).
Magnesium Atoms Oxygen Atoms Molecules of magnesium oxide Summary element compound atom molecule
Which are molecules and which are compounds?
A MIXTURE is a material made up of at least two substances which may be elements or compounds that are NOT chemically bonded.
Properties of Mixtures The composition of a mixture is variable. Each of its components retains its characteristic properties. No chemical reaction is involved Its components are easily separated (e.g. filtration, evaporation).
A mixture in which one substance (solute) is dissolved in another (solvent) and the molecules are evenly distributed. SOLUTION Image source:
Salt Solution Image source:
Post-Lab: Physical Changes
Activity 1. Evaporation of Liquids Describe what happens to the particles during this process. Explain why this happens. Evaporation happens when atoms or molecules escape from the liquid and turn into a vapor.
What factors can affect the rate of evaporation? The energy you can measure with a thermometer is an average of all the molecules in the system. There are always a few molecules with a lot of energy and some with barely any energy at all.
Alcohol WaterOil NATURE OF THE SUBSTANCE Some liquids have __________ forces that hold particles together allowing some particles to escape.
What factors can affect the rate of evaporation? The molecules with a lot of energy are able to build up enough power to become a gas. Once they reach that energy level, they can leave the liquid and thus, it has evaporated. Force of air pressing down
Image source: Factors affecting the rate of evaporation
Applying Understanding: Real-life situations Why do you spread out your wet clothes to dry? Why do you feel cool when you stand next to a fan? Why do you feel cold when you immediately step out of the shower? Why is it important to “ rehydrate? Relate “sweating” to evaporation and our body’s ability to regulate temperature.
FREEZING POINT Change in phase from liquid to solid Why? When energy is taken out from a liquid, particles slow down until forces of attraction cause them to fuse and form a solid. Image source: freezing-point-of-water/ Particles of a liquid Particles slow down Particles fuse
Why is salt added to a snow-covered driveway?
Salt dissolves in water pretty fast. When you sprinkle salt on ice, the salt lowers the freezing point of the water, keeping it from re-freezing as easily and helping to melt the rest of the ice. This is called lowering the freezing point.
When you add salt to water, the salt (called sodium chloride, NaCl) dissolves into particles (actually called ions of sodium and chloride). The freezing point of water becomes lower as more particles are added until the point where the salt stops dissolving. On a driveway or street, sodium chloride can melt ice only down to about (-9°C). ment/how-does-salt-melt-ice
BOILING POINT Evaporation takes place at surface of liquids Boiling takes place beneath surface of liquid Animated GIF "Boiling" - Courtesy of General Chemistry Help - Purdue University"Boiling" Image source: This animation shows how water molecules are able to break the forces of attraction. This is what is happening inside the gas bubble as it is rising to the surface to break and release the water gas molecules. In a liquid, molecules are packed closely together. As a liquid is heated, the temperature is increased. As the temperature increases, the kinetic energy increases which causes increasing motion. Eventually molecules break free of liquid and become a gas. At the temperature of the boiling point, the liquid turns into a gas.
Activity 2. Boiling Point of Liquids How does a coolant help prevent overheating? Car Engine Increases a liquid’s boiling point
How can you make water boil below 100° C?
Vacuum Chamber How does pressure affect the boiling point?
Physics in the Kitchen
How does a pressure cooker work?
Physics in the Kitchen It is the high temperature that cooks the food. Pressure affects boiling. Increased pressure raises the BP. Pressure cookers increase the pressure inside and prevent boiling. The increased temperature cooks food faster.
Never boil water in a Microwave Source: A man decided to have a cup of instant coffee, so he heated a cup of water in the microwave. When the timer went off, he removed the cup from the microwave and noticed that the water had not boiled. Just then, the water literally “blew up” in his face. His whole face was blistered with first and second degree burns, which left some permanent scaring and damage to his left eye. While at the hospital, the doctor attending him stated that his is a fairly common occurrence. Water (alone) should never be heated in a microwave oven.
Never boil water in a Microwave Source: Why? This phenomenon is known as superheating. It can occur anytime water is heated - especially if the cup or bowl is new. What happens is that the water heats faster than the vapor bubbles can form. If the cup is very new, then it is unlikely to have small surface scratches in it that provide a place for the bubbles to form (called nucleation sites). Without bubbles, the water cannot release the heat that has built up, the liquid does not boil, and it continues to heat up past its boiling point. If the water is bumped or jarred, it's enough of a shock to cause the bubbles to rapidly form and the result is an exploding liquid that is scalding hot. One solution is to place a wooden stir stick or something non- metallic in the water to help spread the energy as it is heating in the microwave.
Sublimation and Deposition Solid to gaseous form, or vapor Deposition (Formation of Frost) Deposition (Formation of Frost) Frost-Free Freezers
MELTING POINTS o.nz/gamesactivities/mel tingpoints.htmlhttp://www.sciencekids.c o.nz/gamesactivities/mel tingpoints.html Melting Points temperature at which it changes from a solid to a liquid.
The melting point allows chemists/industrial engineers to create alloys that would be far much stronger than the original materials that are being melted. Steel is an alloy. Most of the stuff that we use - e.g., tennis rackets, bedframes - are alloys - and melting points allow for the creation of these alloys.
How Do Satellites And Launch Vehicle Stages "Breakup" During Reentry From Orbit? The breakup of reentering objects typically occurs around an altitude of 45 to 50 miles ( km) above the Earth's surface. Low melting point materials melt first, exposing other objects to the extreme heat and forces of reentry. As pieces melt or break away, the heating and deceleration loads increase, further breaking the object apart and creating multiple pieces of debris. The debris forms meteor-like streaks in the sky. Some of the debris survives and impacts the Earth's surface along a footprint that can be hundreds of miles long. What Happens To An Object During Reentry? Crewed space vehicles have protective heat shields, allowing them to survive reentry and land on the ground. Most objects however, such as satellites and launch vehicle stages, lack protective shielding. These objects burn and break apart during reentry. Source:
Summary: States or Phases of Water The Phase or State of matter is a physical characteristic. It describes a PHYSICAL state of matter. As matter changes from one state or phase of matter to another, a physical change occurs. If energy is added (like increasing the temperature or increasing pressure) or if energy is taken away (like freezing something or decreasing pressure) those are physical changes.
w/au_sch_whalley_sf1_1/int/2_slg.html Animation- particles and sublimation
Matter changes whenever energy is added or taken away. Energy is added: Solid Liquid Gas Energy is removed: Gas Liquid Solid
States of MatterPhase Change Energy Movement During Phase Change Energy IN or Out Temperature Change During Phase Change Solid to liquidMeltingEnergy into solidNone Liquid to solidFreezingEnergy out of liquid None Liquid to gasVaporization, which includes boiling and evaporation Energy into liquidNone Gas to liquidCondensationEnergy out of gasNone Solid to gasSublimationEnergy into solidNone
Why is melting (solid to liquid) and vaporization (liquid to gas) considered a cooling process? To change from a solid to a liquid or a liquid to a gas requires an increase in the KE of the matter. This KE comes from the environment. A loss of KE from the environment lowers the temp of the environment resulting in a cooling process.
Why is freezing (liquid to solid) and condensation (gas to liquid) considered a heating process? To change a gas to liquid or a liquid to solid requires a decrease in the KE of the matter. This decrease in KE results in a warming process.